EP1066473B1 - Improved self-tapping thread fastener and a blank therefor - Google Patents
Improved self-tapping thread fastener and a blank therefor Download PDFInfo
- Publication number
- EP1066473B1 EP1066473B1 EP99959634A EP99959634A EP1066473B1 EP 1066473 B1 EP1066473 B1 EP 1066473B1 EP 99959634 A EP99959634 A EP 99959634A EP 99959634 A EP99959634 A EP 99959634A EP 1066473 B1 EP1066473 B1 EP 1066473B1
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- European Patent Office
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- section
- thread
- forming
- blank
- main body
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- 238000010079 rubber tapping Methods 0.000 title claims abstract description 17
- 230000000087 stabilizing effect Effects 0.000 claims abstract description 49
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Images
Classifications
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
- B21K1/00—Making machine elements
- B21K1/56—Making machine elements screw-threaded elements
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21K—MAKING FORGED OR PRESSED METAL PRODUCTS, e.g. HORSE-SHOES, RIVETS, BOLTS OR WHEELS
- B21K1/00—Making machine elements
- B21K1/44—Making machine elements bolts, studs, or the like
- B21K1/46—Making machine elements bolts, studs, or the like with heads
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
- F16B25/001—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed
- F16B25/0021—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by the material of the body into which the screw is screwed the material being metal, e.g. sheet-metal or aluminium
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
- F16B—DEVICES FOR FASTENING OR SECURING CONSTRUCTIONAL ELEMENTS OR MACHINE PARTS TOGETHER, e.g. NAILS, BOLTS, CIRCLIPS, CLAMPS, CLIPS OR WEDGES; JOINTS OR JOINTING
- F16B25/00—Screws that cut thread in the body into which they are screwed, e.g. wood screws
- F16B25/0036—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by geometric details of the screw
- F16B25/0078—Screws that cut thread in the body into which they are screwed, e.g. wood screws characterised by geometric details of the screw with a shaft of non-circular cross-section or other special geometric features of the shaft
Definitions
- This invention relates to threaded fasteners and more particularly to self-tapping fasteners that form internal threads using a roll-forming process.
- Self-tapping fasteners that form threads by deforming a thread pattern within a pilot hole have become increasingly popular. There are many advantages to using a roll-forming thread, rather than a more-traditional thread-cutting design.
- a very successful style of roll-forming thread is the multiple-lobed fastener shown, for example, in Phipard, US Patent Nos. 3,195,156 and 3,918,345.
- Such fasteners are available from a variety of sources carrying the trademark TRILOBULAR, in connection with a three-lobe thread-forming blank design.
- Figs 1-5 illustrate a conventional three-lobed thread-forming blank 10 and a resulting fastener (21) according to the prior art (US A 4 042 342).
- a blank 10 is first provided with a head 12 as detailed.
- the head, 12 in this example is a standard hexagonal washer head design. However any other head configuration enabling the driving of the fastener in a rotary fashion about a central axis 14 can be formed.
- the head is formed by striking the end of a straight blank "wire" segment using header punches that forcibly deform one end of a metallic wire made of steel or another hard metal.
- a header die deforms a specialized tapered thread-forming and stabilizing section on the opposite end (the "tip") of the shaft.
- the wire at the time of head and tip formation, typically already has a lobular cross-section 16 as revealed in Fig. 3.
- Each lobe 18 is, in essence, an "out-of-round” formation.
- the lobes present an eccentric cross section with respect to an otherwise round shape.
- formation of the blank, prior to forming the head involves the drawing of a round-cross-section wire through a lobed female die to create the illustrated out-of-round on the main body of the blank (10).
- the headed blank 10 is passed between a pair of forming dies to form thereon a set of external threads 22 detailed generally in Fig. 4. These threads exhibit the out-of-round characteristics of the blank.
- the external apices 24 of each thread are located at an outer diameter greater than that of the original blank, since material has been displaced from the thread troughs 26 outwardly at predetermined locations to form each apex.
- All threads have a characteristic pitch and diameter. Because of the lobulation of the threads, the radial offset from the axis 14 will vary about the circumference. In general, standard thread diameters and pitches are provided to lobular fasteners, but the lobes tend to have a slightly larger diameter than a standard thread diameter. This enables the lobes to positively form corresponding internal threads as the self tapping fastener is driven into an appropriately-sized pilot hole to form internal threads.
- the threaded fastener 21 is provided with a discrete stabilizing zone 30 having stabilizing threads 32, and a thread-forming zone 33 with corresponding thread-forming threads 34.
- the stabilizing zone 30, as detailed in Figs. 1 and 2, has a reduced diameter, enabling it to fit within an untapped pilot hole in a relatively perpendicular fashion.
- the thread-forming zone 33 has a sloped/tapered shape with diameter that increases linearly between the stabilizing zone and the full-diameter main body 20.
- the thread stabilizing zone 30 has a higher out-of-round section than the main body 20. This is clear from the end-on view of Fig. 2.
- the thread forming zone 33 also has a higher out-of-round configuration than the full-diameter main body 20.
- the out-of-round of the thread forming zone gradually tapers back from the highest out-of-round adjacent to the stabilizing zone toward the lower out-of-round that defines the full-diameter main body 20.
- the thread forming zone can define an approximately constant-profile high out-of-round configuration along its entire axial length, that transitions stepwise at the main body into the characteristic lower out-of-round. In connection with either example, note the difference between the high out-of-round at the stabilizing section end (Fig. 2) and at the main body cross section (Fig. 3).
- the thread-forming threads 34 encounter the sidewalls of the hole initially. These threads exhibit an increasing outer diameter and higher out-of-round configuration. As such, the lobes are able to gradually apply increasing thread-forming pressure to the pilot hole until each formed internal thread is contacted by the first full-diameter thread 40.
- This first full-diameter thread 40 has the out-of-round profile of the rest of the main body. It provides the final formation of each thread in the pilot hole to the desired shape.
- This invention overcomes the disadvantages of the prior art by providing a blank, and corresponding fastener with a cross section that defines a series of lobes, and that has an additional thread-forming axial section between the lobed tapered thread-forming section and the full-diameter lobed main body of the blank.
- This additional thread forming section is also substantially full-diameter and exhibits cross sectional lobes with a higher out-of-round than those of the main body blank/threads.
- the additional thread-forming section has an axial length of approximately one thread pitch, thereby providing one additional high-out-of-round full-diameter thread forward of (in a head-to-tip direction) the main body threads.
- the lobes of the additional thread-forming thread are located at the full diameter, like the adjacent main body threads, but have a higher contact pressure due to less material in contact with the internal threads being formed. As such the additional full-diameter thread-forming thread applies more thread-forming pressure than would be applied by a conventional main body thread at the same axial position.
- the invention in its broad form resides in a self tapping screw blank and in a self tapping screw fastener with self tapping threads and of the type having a head portion and a tip portion; a noncircular main cross section with an axis and a plurality of radial lobes and valley portions between the radial lobes, said cross section having an out-of-round attribute K which is a difference between a maximum radial dimension from the axis to a peak of a radial lobe and a second radial least dimension from the axis to a lowest valley portion; a pitch 'P' which is an axial distance between corresponding regions of consecutive threads; a main body portion of the self-tapping screw adjacent to the head portion and being of a predetermined diameter; a tapered thread-forming-section adjacent the tip portion and of diameter which tapers down from said predetermined diameter towards said tip portion a first predetermined value of K for the main body portion, and a second value of K for the tapered thread forming
- the invention also teaches a method of forming a screw fastener blank using a header die, the blank being of the type having (i) a head portion and a tip portion, (ii) a noncircular cross section with an axis and a plurality of circumferentially spaced radial lobes and valley portions between the radial lobes, said noncircular cross section having an out-of-round attribute K which is a difference between a first maximum radial dimension measured from the axis to a peak of a radial lobe and a second least radial dimension measured from the axis to a lowest valley portion, said method comprising using a forming die cavity including walls for forming a main body portion of the screw fastener blank adjacent to the head portion and being of a predetermined diameter; a tapered thread-forming-section adjacent the tip portion and of diameter which tapers down from said predetermined diameter towards said tip portion; said die cavity having a first predetermined value of K for the main body portion, and
- a fastener blank having a cross section, taken through an axis, that defines at least three lobes and three valleys therebetween, the lobes having a lobe maximum diameter with respect to the axis and the valleys having a valley maximum diameter with respect to the axis, the lobe maximum diameter being larger than the valley maximum diameter, and a relationship therebetween being defined by an out-of round dimension
- the blank comprising a main body section extending in an axial direction from a drive head toward a tip, the main body section having main body valleys with a main body valley maximum diameter and main body lobes with a main body lobe maximum diameter and defining therebetween a main body section out-of-round dimension; a tapered thread-forming section located forward, taken in the axial direction toward the tip, of the main body section, the tapered thread-forming section having, at each axial point therealong, tapered thread-forming section valleys with a tapered thread-forming valley maximum diameter and tapered thread-forming
- the blank can include the above-described higher out-of-round section on a blank that includes a tapered section, but no substantial stabilizing section forward thereof.
- the additional thread-forming section has an out-of-round defined by the out-of-round factor K (further defined hereinbelow) equal to approximately 0.2-0.3 times the relative thread pitch while the out-of-round of the main body threads is maintained at a factor K approximately 0.05-0.15 times the relative pitch.
- a blank having the above-described thread forming and main body sections can be formed to selectively include either a stabilizing section or a tip that begins at the tapered section by providing a header die with a knock-out pin in which the knock-out pin can be positioned to occupy or reveal part of a forming die cavity therein that conforms to the size and shape of the stabilizing section.
- Fig. 6 illustrates a fastener blank according to a preferred embodiment of this invention.
- the blank 100 includes a drive head 102 having any suitable desired shape. As described above, the head may be formed on the blank using header punches or another acceptable method.
- the blank 100 is formed preferably from a hardenable metal such as low-medium carbon steel. Final hardening is typically accomplished in the form of heat treating, case hardening, magnetic induction hardening, nitride coating and the like after final thread formation on the blank has been completed.
- the blank in this embodiment includes three discrete lobes like those shown with reference to Figs. 1-5. If desired, more lobes can be used. It has been found, however, that three lobes are optimal. When more lobes are used, it is preferable that the number of lobes be odd.
- the blank 100 includes a main body 104, a stabilizing section 106, a tapered thread-forming section 108 and a unique additional thread-forming section 110.
- the length of each section, 104, 106, 108 and 110 (LM, LS, LT and LA, respectively) of the blank is herein defined preferably in terms of the number of standard pitch lengths that can be applied to the respective fastener blank section as it is formed.
- a lobular fastener can be formed in accordance with the teachings of Phipard, Jr., US patent No. 3,918,345, (see, for example, Fig. 5 therein) using a pair of forming dies that are moved in predetermined opposite directions in which a headed blank is passed therebetween.
- the forming dies include linear grooves that conform to thread shapes and are set at an appropriate pitch spacing from each other.
- the forming dies define curved or angled/inclined surfaces that taper toward each other near the tip of the blank (opposite the head), conforming with the tapered thread-forming and stabilizing zone of the associated blank.
- the dies are first brought into compressive, permanently deforming contact with the blank, one die contacting a lobe, and the other contacting an opposing valley on the three-lobe, three-valley blank.
- the threads are pressed into the contact points at this time.
- the blank is rotated between them with its center axis 112 defining an oscillating path. This oscillation corresponds to the rotation of the blank about its lobes.
- the dies maintain a constant spacing as they move, forming a thread pattern of predetermined depth (based upon the degree of radial die separation) on the blank surface.
- the finished fastener which is shown in Fig. 7 including threads will include a set of main body threads 120 that are substantially even in pitch and diameter.
- the stabilizing threads 122 which are typically 1 1/2-3 pitches in length (length LS), are smaller in diameter.
- two to three forming threads are provided in this embodiment (length LT).
- three-four forming threads are provided.
- the stabilizing and thread-forming blank sections 106 and 108, respectively, and the corresponding threads 122, 124, 126 and 128 define an out-of-round section that is larger than that of the main body 104 and its threads 120. This is, as noted above, desired to reduce the thread-forming torque required when the fastener is driven into an unthreaded pilot hole.
- a technique for defining out-of-round in a multi-lobe fastener blank is described. This measurement technique is detailed generally in Fig. 10.
- the cross-sectional outline 150 of the blank corresponds to an odd-numbered polygon. In this case it is a triangle.
- the triangle is circumscribed about the central axis 112.
- the individual curved segments that make up the outline 150 are particularly defined according to known conventions described, for example, in the Phipard patents noted above. Definitions of the outline shape are also available in a variety of literature related to TRILOBULARTM fasteners available from Research Engineering and Manufacturing, Inc. of Middletown, Rhode Island, USA.
- a circle 152 is shown circumscribing each apex or comer 154 of the outline 150. This is a circle of maximum diameter for the blank. It is centered about the axis 112.
- Another circle 156, also centered about the axis 112 contacts the most inwardly located valley 158 of the outline 150 with respect to the axis 112.
- the diameter of the outer circle 152 is denoted as C.
- the distance between an apex 154 and an opposing valley 158 is denoted as D.
- the difference between C and D is denoted as the dimension value K.
- K is, in essence, the magnitude of the out-of-round dimension inherent in a given blank cross section.
- the main body 104 is provided with a dimension K that is relatively low, being 0.05-0.15 times the relative thread pitch P.
- the out-of-round dimension of the thread-forming section 108, and associated threads 124, 126 and 128 are defined by a K approximately 0.20-0.30 times the thread pitch P.
- the additional thread-forming section 110 which has an axial length LA of approximately one pitch length (P) maintains the out-of-round dimension of the adjacent portion 160 of the tapered thread-forming section 108.
- a thread 162 is defined on the section 110 that has a relatively high out-of-round or K equal to 0.20-0.30 times the pitch P of the fastener thread.
- the section 110 can have an axial length sufficient to accommodate two or more full-diameter thread-forming threads thereon, according to an alternative embodiment of this invention.
- the diameter of the lobes of this thread are substantially the same as those of the adjacent main body threads.
- the zone 110 presents a full-diameter forming profile to the internal threads, but does so at a higher pressure intensity, since less area on each lobe of the thread 162 in additional zone 110 is in contact with the internal thread.
- the next adjacent thread 170 among the main body threads 120 has an abruptly reduced out-of-round dimension with a K equal to 0.05-0.15 in this embodiment.
- the torque necessary to form a thread in a pilot hole is substantially reduced.
- the thread 162 acts as a full diameter transition thread that still maintains a high contact pressure for final formation of threads at full diameter.
- Figs. 8 and 9 show a fastener blank and resulting threaded fastener according to alternative embodiment. Unlike the embodiment shown in Figs. 6 and 7, the embodiment detailed in Figs. 8 and 9 does not include a stabilizing section. In some applications, a stabilizing section is not necessary nor desired.
- the blank includes a main body 204 having a length L1M; also shown is a tapered thread-forming section 206 having a length L1T and an additional section 208 disposed axially between the tapered thread-forming section 206 and main body section 204.
- the additional section has an axial length L1A.
- a relatively small tip portion 210 [usually 0.25mm to 0.36mm (010-0.015 inch) in axial length] is also depicted. This is excess material displaced during the tip formation process in the header die and is not significant to the structure defined herein as described above. In particular, the tip often serves as an indicator that shows whether the full section of the header die has been filled out during blank manufacture.
- the axial length of the main body 204 varies depending upon the desired length of the fastener. As shown in Fig. 9, a series of main body threads 220 are defined on the main body using the thread die-forming process described above. The out-of-round aspect K for these threads is approximately 0.05-0.15 times the pitch P1.
- Three diametrically increasing thread-forming threads 224, 226 and 228 are also formed. Their out-of-round aspect K, as defined above, is equal to 0.20-0.30 times P1.
- the length L1T of the tapered thread-forming section is sufficient, as illustrated, to provide approximately three threads thereon.
- the additional thread-forming thread 230 formed on the additional section 208 has the high out-of-round aspect K equal to 0.20-0.30 times P1, and provides the full-diameter thread-forming transition into the main body threads.
- the additional section length L1A is, of course, sufficient to provide one thread pitch at minimum.
- a hard header die 300 is shown. It defines a forming die cavity 302, into which fastener blank material in the form of a cut-off piece of wire or rod 304 of predetermined size is placed.
- the die cavity 302 is a dimensioned hole that conforms to the desired finished blank shape.
- the die cavity 302 has sidewalls of sufficient thickness and hardness to ensure that no deformation of the die cavity 302 will occur as a piece of wire or rod is driven thereinto to be plastically deformed into the blank shape.
- the cross section of the die cavity 302 (not shown), of course, defines three or more lobes as described above.
- the wire or rod section used to form the blank can also include three or more conforming lobes.
- the wire or rod typically has a cross section that conforms to the desired main body shape so further forming of this main body portion of the blank is minimal.
- the die 300 is formed according to conventional techniques, using known materials and dimensional sizing for sidewall thickness, etc.
- Formation of a finished fastener blank often occurs in several strikes applied by a ram or punches 305 (shown in phantom).
- the punches are preferably driven by a powerful mechanical actuator (not shown) that strikes the blank under great pressure (see arrow 307) to cause both the blank head and internal blank shape to be formed simultaneously.
- a powerful mechanical actuator not shown
- Several differently shaped punches and/or header dies can be used progressively during formation of the blank and blank head, each with a shape that conforms progressively more closely to that of the finished blank drive head 102.
- that drive head 102 takes the form of a conventional hex washer head shape as shown above.
- the tools/punches used herein are considered conventional.
- the die cavity 302 defines the distinct shapes of the blank sections according to each of the embodiments of this invention.
- the die cavity 302 defines a series of shaped sections that form the respective sections of the finished fastener blank through plastic deformation as the initial rod or wire is driven into the die cavity by the punch 305.
- the sections each define a multi-lobed cross section having the desired out-of-round configuration as discussed above.
- the die cavity sections include an elongated main body die cavity section 306 for enclosing the blank's corresponding main body adjacent the opening of the die cavity.
- the neighboring full-diameter, high out-of-round thread forming section 312 having a high out-of round is located inwardly of the main body die cavity section 306.
- the tapered thread forming die cavity section 312 and stabilizing section die cavity section 316 are each located further inwardly, respectively.
- the rod or wire is seated inwardly as far as it can go. It typically seats onto the front of the full-diameter thread forming section 312.
- Each strike of the punch or punches causes the rod or wire tip to deform into the next forward section as it is driven further into the die cavity.
- a knock-out pin acts as a stop to prevent further inward movement of the blank into the die cavity 302.
- This pin is formed from a hardened material according to known processes. It can move axially inwardly and outwardly (double arrow 348) under the force of a mechanical actuator (not shown) of known design.
- the knock-out pin includes a mechanism that can be locked into position (not shown) so as to maintain its position firmly when it is acting as a stop as shown in Figs 11 and 12.
- the knock out pin is moved toward the cavity front opening a sufficient distance to eject the blank.
- the blank can then be transferred by known techniques to another cavity for further forming or to a threading mechanism or machine for forming of the threads.
- Fig. 12 illustrates the die 300 configured to form a blank (200) according to the embodiment detailed in Figs. 8 and 9.
- This blank is substantially similar in size and shape to the blank (100) described above. However, it omits a stabilizing section at its front.
- the knock-out pin can be selectively moved (double arrow 348) toward and away from the front opening of the die cavity 302. Hence, the knock out pin can be moved by its actuator to selectively occupy the area of the stabilization section die cavity 316.
- the knock-out pin 330 advantageously has a cross section that matches that of the cavity. To create a blank 100 according to Figs. 6, 7 and 11, the knock-out pin is positioned approximately 1 1/2-3 pitch lengths forwardly of the tapered thread forming section 314.
- the blank can include further forming and stabilizing sections, in addition to the full-diameter forming section detailed herein.
- a variety of other forming techniques can be used to form blanks, drive heads and thread patterns including fully enveloping dies, cutting tools or rolling dies.
- the thread profile depicted herein is of a conventional triangular/straight-line configuration. It is expressly contemplated that a blank according to this invention can be provided with any kind of thread profile including a curved/radius profile, a cupped profile, buttress profile or a square/Acme profile.
- K factors for out-of-round are specified hereinabove for various blank sections, it is expressly contemplated that these values can be varied for applications having particular size, shape and material requirements.
- the exact K factor can be determined for such an application using data based upon physical tests and experiments on fasteners formed with a given set of properties. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of the invention.
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Abstract
Description
- This invention relates to threaded fasteners and more particularly to self-tapping fasteners that form internal threads using a roll-forming process.
- Self-tapping fasteners that form threads by deforming a thread pattern within a pilot hole have become increasingly popular. There are many advantages to using a roll-forming thread, rather than a more-traditional thread-cutting design. A very successful style of roll-forming thread is the multiple-lobed fastener shown, for example, in Phipard, US Patent Nos. 3,195,156 and 3,918,345. Such fasteners are available from a variety of sources carrying the trademark TRILOBULAR, in connection with a three-lobe thread-forming blank design.
- Figs 1-5 illustrate a conventional three-lobed thread-forming blank 10 and a resulting fastener (21) according to the prior art (US A 4 042 342). In manufacturing a threaded fastener, a blank 10 is first provided with a
head 12 as detailed. The head, 12 in this example is a standard hexagonal washer head design. However any other head configuration enabling the driving of the fastener in a rotary fashion about acentral axis 14 can be formed. The head is formed by striking the end of a straight blank "wire" segment using header punches that forcibly deform one end of a metallic wire made of steel or another hard metal. As will be described further a header die deforms a specialized tapered thread-forming and stabilizing section on the opposite end (the "tip") of the shaft. The wire, at the time of head and tip formation, typically already has alobular cross-section 16 as revealed in Fig. 3. Eachlobe 18 is, in essence, an "out-of-round" formation. In other words, the lobes present an eccentric cross section with respect to an otherwise round shape. In fact, formation of the blank, prior to forming the head involves the drawing of a round-cross-section wire through a lobed female die to create the illustrated out-of-round on the main body of the blank (10). The headed blank 10 is passed between a pair of forming dies to form thereon a set ofexternal threads 22 detailed generally in Fig. 4. These threads exhibit the out-of-round characteristics of the blank. In general, theexternal apices 24 of each thread are located at an outer diameter greater than that of the original blank, since material has been displaced from thethread troughs 26 outwardly at predetermined locations to form each apex. - All threads have a characteristic pitch and diameter. Because of the lobulation of the threads, the radial offset from the
axis 14 will vary about the circumference. In general, standard thread diameters and pitches are provided to lobular fasteners, but the lobes tend to have a slightly larger diameter than a standard thread diameter. This enables the lobes to positively form corresponding internal threads as the self tapping fastener is driven into an appropriately-sized pilot hole to form internal threads. - In other words, as the fastener 21 (Figs. 4 and 5) is rotated clockwise, the lobes engage the inner wall of the pilot hole (not shown) and begin to displace material within the pilot hole. The threaded
fastener 21 is provided with a discrete stabilizingzone 30 having stabilizingthreads 32, and a thread-formingzone 33 with corresponding thread-formingthreads 34. The stabilizingzone 30, as detailed in Figs. 1 and 2, has a reduced diameter, enabling it to fit within an untapped pilot hole in a relatively perpendicular fashion. The thread-formingzone 33 has a sloped/tapered shape with diameter that increases linearly between the stabilizing zone and the full-diametermain body 20. Note that thethread stabilizing zone 30 has a higher out-of-round section than themain body 20. This is clear from the end-on view of Fig. 2. Thethread forming zone 33 also has a higher out-of-round configuration than the full-diametermain body 20. In one example, the out-of-round of the thread forming zone gradually tapers back from the highest out-of-round adjacent to the stabilizing zone toward the lower out-of-round that defines the full-diametermain body 20. In another, usually preferred example, the thread forming zone can define an approximately constant-profile high out-of-round configuration along its entire axial length, that transitions stepwise at the main body into the characteristic lower out-of-round. In connection with either example, note the difference between the high out-of-round at the stabilizing section end (Fig. 2) and at the main body cross section (Fig. 3). - As a fastener is driven into an untapped pilot hole, the thread-forming
threads 34 encounter the sidewalls of the hole initially. These threads exhibit an increasing outer diameter and higher out-of-round configuration. As such, the lobes are able to gradually apply increasing thread-forming pressure to the pilot hole until each formed internal thread is contacted by the first full-diameter thread 40. This first full-diameter thread 40 has the out-of-round profile of the rest of the main body. It provides the final formation of each thread in the pilot hole to the desired shape. - In general, to form a thread properly requires several swaging "blows" from the underlying lobes of the fastener. This process is, in essence, similar to the formation of a shape in a ductile metal by a blacksmith's hammer. A sufficient number of forming threads is necessary to complete the process. To make the process go more quickly, a high out-of-round configuration, which concentrates the force of the blows is desirable. Use of a high out-of-round configuration within the main, full-diameter threads substantially reduces the amount of torque that must be applied to form threads. However, this lower torque comes at a price, since it results in less diametrical material remaining in contact with the internal thread once it is formed. Hence, it is more likely that failure will occur in such a fastener system. Such failure, in general, results from axial pull-out or, when thicker nut members are used, fracture. Also, since the fastener cross sectional area varies as the square of the radius, the use of a higher out-of-round cross section results in a significantly reduced cross sectional area, which lowers the failure limit of the fastener. Hence, self-tapping screws typically use an out-of-round dimension that is a compromise between the optimum value for thread forming efficiency and the optimum value for resistance to failure.
- Previous attempts to balance a desire for higher out-of-round section, versus failure resistance is described in US Patent No. 4,040,328 to Muenchinger. This patent provides a tapered point zone on the fastener with stabilizing threads that have a higher out-of-round section than the fastener body. However, the out-of-round of the stabilizing threads is, in fact, significantly greater than that of the full-forming thread. This is a less efficient structure, since the stabilizing and thread-forming threads are tasked with virtually all the forming work, while the first full-diameter thread has the lower out-of-round cross section, which is inefficient for thread forming purposes.
- It is therefore an object of this invention to provide a fastener blank, and underlying threaded fastener formed therefrom, that exhibits relatively low thread-forming torque, while maintaining good resistance to failure, in use, in engagement within a nut-member or other thread-formed hole.
- This invention overcomes the disadvantages of the prior art by providing a blank, and corresponding fastener with a cross section that defines a series of lobes, and that has an additional thread-forming axial section between the lobed tapered thread-forming section and the full-diameter lobed main body of the blank. This additional thread forming section is also substantially full-diameter and exhibits cross sectional lobes with a higher out-of-round than those of the main body blank/threads. The additional thread-forming section has an axial length of approximately one thread pitch, thereby providing one additional high-out-of-round full-diameter thread forward of (in a head-to-tip direction) the main body threads. The lobes of the additional thread-forming thread are located at the full diameter, like the adjacent main body threads, but have a higher contact pressure due to less material in contact with the internal threads being formed. As such the additional full-diameter thread-forming thread applies more thread-forming pressure than would be applied by a conventional main body thread at the same axial position.
- The invention in its broad form resides in a self tapping screw blank and in a self tapping screw fastener with self tapping threads and of the type having a head portion and a tip portion; a noncircular main cross section with an axis and a plurality of radial lobes and valley portions between the radial lobes, said cross section having an out-of-round attribute K which is a difference between a maximum radial dimension from the axis to a peak of a radial lobe and a second radial least dimension from the axis to a lowest valley portion; a pitch 'P' which is an axial distance between corresponding regions of consecutive threads; a main body portion of the self-tapping screw adjacent to the head portion and being of a predetermined diameter; a tapered thread-forming-section adjacent the tip portion and of diameter which tapers down from said predetermined diameter towards said tip portion a first predetermined value of K for the main body portion, and a second value of K for the tapered thread forming section, said second value of K being greater than said first predetermined value of K, an improvement comprising an additional thread forming section located between the main body portion and the tapered thread-forming-section, and being of axial length capable of accommodating at least one thread, said additional thread forming section having the same predetermined diameter as said main body portion and having substantially the same value of K as the tapered thread forming section.
- The invention also teaches a method of forming a screw fastener blank using a header die, the blank being of the type having (i) a head portion and a tip portion, (ii) a noncircular cross section with an axis and a plurality of circumferentially spaced radial lobes and valley portions between the radial lobes, said noncircular cross section having an out-of-round attribute K which is a difference between a first maximum radial dimension measured from the axis to a peak of a radial lobe and a second least radial dimension measured from the axis to a lowest valley portion, said method comprising using a forming die cavity including walls for forming a main body portion of the screw fastener blank adjacent to the head portion and being of a predetermined diameter; a tapered thread-forming-section adjacent the tip portion and of diameter which tapers down from said predetermined diameter towards said tip portion; said die cavity having a first predetermined value of K for the main body portion, and a second value of K for the tapered thread forming section, said second value of K being greater than said first predetermined value of K, said die cavity including an additional thread forming section located between the main body portion and the tapered thread-forming-section and being of axial length capable of accommodating at least one thread, said additional thread forming section having the same predetermined diameter as said main body portion and having substantially the same value of K as the tapered thread forming section, the method including the step of using a selectively positionable knock-out pin that stops linear movement of the blank beyond a predetermined axial point during formation, the knock-out pin being constructed and arranged to selectively uncover and reveal a stabilizing section forming die cavity axially forward of a part of the die cavity that forms the tapered thread-forming section, the stabilizing section forming die cavity being constructed and arranged to form a blank stabilizing section with a lower stabilizing lobe maximum diameter than the main body lobe maximum diameter.
- Also taught herein is a fastener blank having a cross section, taken through an axis, that defines at least three lobes and three valleys therebetween, the lobes having a lobe maximum diameter with respect to the axis and the valleys having a valley maximum diameter with respect to the axis, the lobe maximum diameter being larger than the valley maximum diameter, and a relationship therebetween being defined by an out-of round dimension, the blank comprising a main body section extending in an axial direction from a drive head toward a tip, the main body section having main body valleys with a main body valley maximum diameter and main body lobes with a main body lobe maximum diameter and defining therebetween a main body section out-of-round dimension; a tapered thread-forming section located forward, taken in the axial direction toward the tip, of the main body section, the tapered thread-forming section having, at each axial point therealong, tapered thread-forming section valleys with a tapered thread-forming valley maximum diameter and tapered thread-forming valley lobes with a tapered thread-forming lobe maximum diameter and defining therebetween a tapered thread-forming section out-of-round dimension, the main body section out-of round dimension being lower than the tapered thread-forming section out-of-round dimension; and a full-diameter thread-forming section located axially between the main body section and the tapered thread-forming section, the full diameter thread forming section having full-diameter thread-forming section valleys with a full-diameter thread-forming valley maximum diameter and full-diameter thread-forming valley lobes with a full-diameter thread-forming lobe maximum diameter and defining therebetween a full-diameter thread-forming section out-of-round dimension, wherein the full-diameter thread-forming lobe maximum diameter is approximately equal to the main body lobe maximum diameter and the full-diameter thread-forming out-of-round dimension is higher than the main body out-of-round dimension, whereby the lobes of the full-diameter thread-forming section exerts a higher thread-forming pressure than the lobes of the main body section.
- In an alternative embodiment, the blank can include the above-described higher out-of-round section on a blank that includes a tapered section, but no substantial stabilizing section forward thereof. In each of the above embodiments, the additional thread-forming section has an out-of-round defined by the out-of-round factor K (further defined hereinbelow) equal to approximately 0.2-0.3 times the relative thread pitch while the out-of-round of the main body threads is maintained at a factor K approximately 0.05-0.15 times the relative pitch.
- A blank having the above-described thread forming and main body sections can be formed to selectively include either a stabilizing section or a tip that begins at the tapered section by providing a header die with a knock-out pin in which the knock-out pin can be positioned to occupy or reveal part of a forming die cavity therein that conforms to the size and shape of the stabilizing section.
- The foregoing and other objects and advantages of the invention will become more clear with reference to the following description of exemplary embodiments as illustrated by the drawings in which:
- Fig. 1, already described, is a side view of a self-tapping roll-forming fastener blank according to the prior art;
- Fig. 2, already described, is a front-end view of the fastener of Fig. 1;
- Fig. 3, already described, is a cross-section of the fastener blank taken along line 3-3 of Fig. 1;
- Fig. 4, already described, is a broken side view of an exemplary thread pattern formed from the blank of Fig. 1;
- Fig. 5, already described, is a more detailed view of the stabilizing and thread-forming sections of the fastener of Fig. 4;
- Fig. 6 is a side view of a self-tapping roll-forming fastener blank according to an embodiment of this invention;
- Fig. 7 is a side view of an exemplary thread pattern formed on the fastener blank of Fig. 6;
- Fig. 8 is a side view of a self-tapping roll-forming fastener blank according to an alternative embodiment of this invention;
- Fig. 9 is a side view of an exemplary thread pattern formed on the blank of Fig. 8;
- Fig. 10 is a cross section of a typical fastener blank, illustrating a system for measuring an out-of-round configuration;
- Fig. 11 is a cross section of a header die arrangement for producing a blank according to one embodiment of this invention; and
- Fig. 12 is a cross section of the header die arrangement of Fig. 11 for producing a blank according to an alternative embodiment of the invention.
-
- Fig. 6 illustrates a fastener blank according to a preferred embodiment of this invention. The blank 100 includes a
drive head 102 having any suitable desired shape. As described above, the head may be formed on the blank using header punches or another acceptable method. The blank 100 is formed preferably from a hardenable metal such as low-medium carbon steel. Final hardening is typically accomplished in the form of heat treating, case hardening, magnetic induction hardening, nitride coating and the like after final thread formation on the blank has been completed. - The blank in this embodiment includes three discrete lobes like those shown with reference to Figs. 1-5. If desired, more lobes can be used. It has been found, however, that three lobes are optimal. When more lobes are used, it is preferable that the number of lobes be odd.
- The blank 100 includes a
main body 104, a stabilizing section 106, a tapered thread-forming section 108 and a unique additional thread-formingsection 110. The length of each section, 104, 106, 108 and 110 (LM, LS, LT and LA, respectively) of the blank is herein defined preferably in terms of the number of standard pitch lengths that can be applied to the respective fastener blank section as it is formed. - By way of background, a lobular fastener can be formed in accordance with the teachings of Phipard, Jr., US patent No. 3,918,345, (see, for example, Fig. 5 therein) using a pair of forming dies that are moved in predetermined opposite directions in which a headed blank is passed therebetween. The forming dies include linear grooves that conform to thread shapes and are set at an appropriate pitch spacing from each other. Typically, the forming dies define curved or angled/inclined surfaces that taper toward each other near the tip of the blank (opposite the head), conforming with the tapered thread-forming and stabilizing zone of the associated blank. During formation, the dies are first brought into compressive, permanently deforming contact with the blank, one die contacting a lobe, and the other contacting an opposing valley on the three-lobe, three-valley blank. The threads are pressed into the contact points at this time. As a moving die passes by a stationary die, the blank is rotated between them with its
center axis 112 defining an oscillating path. This oscillation corresponds to the rotation of the blank about its lobes. The dies maintain a constant spacing as they move, forming a thread pattern of predetermined depth (based upon the degree of radial die separation) on the blank surface. Note that, during fastener manufacture, a slight degree of thread underfill/overfill may exist given the symmetrical spacing of the dies. This underfill/overfill, which occurs primarily in the stabilizing and thread forming sections of the fastener, does not appreciably affect the performance of the fastener. - The finished fastener which is shown in Fig. 7 including threads will include a set of
main body threads 120 that are substantially even in pitch and diameter. The stabilizing threads 122, which are typically 1 1/2-3 pitches in length (length LS), are smaller in diameter. The thread-formingthreads front end 130 of the fastener to thehead 102. Typically, two to three forming threads are provided in this embodiment (length LT). In an alternative embodiment, three-four forming threads (or more) are provided. As noted above, the stabilizing and thread-forming blank sections 106 and 108, respectively, and thecorresponding threads main body 104 and itsthreads 120. This is, as noted above, desired to reduce the thread-forming torque required when the fastener is driven into an unthreaded pilot hole. With reference again to Phipard, Jr. U.S. Patent '345, a technique for defining out-of-round in a multi-lobe fastener blank is described. This measurement technique is detailed generally in Fig. 10. Thecross-sectional outline 150 of the blank corresponds to an odd-numbered polygon. In this case it is a triangle. The triangle is circumscribed about thecentral axis 112. The individual curved segments that make up theoutline 150 are particularly defined according to known conventions described, for example, in the Phipard patents noted above. Definitions of the outline shape are also available in a variety of literature related to TRILOBULAR™ fasteners available from Research Engineering and Manufacturing, Inc. of Middletown, Rhode Island, USA. Acircle 152 is shown circumscribing each apex orcomer 154 of theoutline 150. This is a circle of maximum diameter for the blank. It is centered about theaxis 112. Anothercircle 156, also centered about theaxis 112 contacts the most inwardly locatedvalley 158 of theoutline 150 with respect to theaxis 112. The diameter of theouter circle 152 is denoted as C. The distance between an apex 154 and an opposingvalley 158 is denoted as D. The difference between C and D is denoted as the dimension value K. K is, in essence, the magnitude of the out-of-round dimension inherent in a given blank cross section. - Referring again to Figs. 6 and 7 the
main body 104 is provided with a dimension K that is relatively low, being 0.05-0.15 times the relative thread pitch P. On the other hand, the out-of-round dimension of the thread-forming section 108, and associatedthreads section 110, which has an axial length LA of approximately one pitch length (P) maintains the out-of-round dimension of theadjacent portion 160 of the tapered thread-forming section 108. In other words, a thread 162 is defined on thesection 110 that has a relatively high out-of-round or K equal to 0.20-0.30 times the pitch P of the fastener thread. It is expressly contemplated, however that, thesection 110 can have an axial length sufficient to accommodate two or more full-diameter thread-forming threads thereon, according to an alternative embodiment of this invention. The diameter of the lobes of this thread are substantially the same as those of the adjacent main body threads. Hence thezone 110 presents a full-diameter forming profile to the internal threads, but does so at a higher pressure intensity, since less area on each lobe of the thread 162 inadditional zone 110 is in contact with the internal thread. Of course there may be slight variations in diameter between the thread 162 and themain body threads 120, but the thread is sufficiently close in diameter to be termed a full-diameter thread with respect to the full diametermain body threads 120. The nextadjacent thread 170 among themain body threads 120 has an abruptly reduced out-of-round dimension with a K equal to 0.05-0.15 in this embodiment. By providing an additional thread 162 having the above-described high out-of-round dimension, with an outer diameter that is essentially the same as the remainder of themain body threads 120, the torque necessary to form a thread in a pilot hole is substantially reduced. Rather than having the thread-forming zone transition immediately into a low out-of-round main body zone, the thread 162 acts as a full diameter transition thread that still maintains a high contact pressure for final formation of threads at full diameter. Hence, when themain body threads 120 finally reach the newly formed internal threads of the pilot hole, they will not be required to exert an overly high formation pressure themselves. - Reference is now made to Figs. 8 and 9 which show a fastener blank and resulting threaded fastener according to alternative embodiment. Unlike the embodiment shown in Figs. 6 and 7, the embodiment detailed in Figs. 8 and 9 does not include a stabilizing section. In some applications, a stabilizing section is not necessary nor desired. Fig. 8, particularly, shows a fastener blank 200 having a head formed 202 thereon of a predetermined shape and size. The blank includes a
main body 204 having a length L1M; also shown is a tapered thread-forming section 206 having a length L1T and an additional section 208 disposed axially between the tapered thread-forming section 206 andmain body section 204. The additional section has an axial length L1A. A relatively small tip portion 210 [usually 0.25mm to 0.36mm (010-0.015 inch) in axial length] is also depicted. This is excess material displaced during the tip formation process in the header die and is not significant to the structure defined herein as described above. In particular, the tip often serves as an indicator that shows whether the full section of the header die has been filled out during blank manufacture. The axial length of themain body 204 varies depending upon the desired length of the fastener. As shown in Fig. 9, a series ofmain body threads 220 are defined on the main body using the thread die-forming process described above. The out-of-round aspect K for these threads is approximately 0.05-0.15 times the pitch P1. Three diametrically increasing thread-formingthreads thread 230 formed on the additional section 208 has the high out-of-round aspect K equal to 0.20-0.30 times P1, and provides the full-diameter thread-forming transition into the main body threads. The additional section length L1A, is, of course, sufficient to provide one thread pitch at minimum. - The formation of a finished blank (100) detailed in Figs. 5 and 6 can be accomplished as shown in Fig. 11. A hard header die 300 is shown. It defines a forming
die cavity 302, into which fastener blank material in the form of a cut-off piece of wire orrod 304 of predetermined size is placed. Thedie cavity 302 is a dimensioned hole that conforms to the desired finished blank shape. Thedie cavity 302 has sidewalls of sufficient thickness and hardness to ensure that no deformation of thedie cavity 302 will occur as a piece of wire or rod is driven thereinto to be plastically deformed into the blank shape. The cross section of the die cavity 302 (not shown), of course, defines three or more lobes as described above. The wire or rod section used to form the blank can also include three or more conforming lobes. The wire or rod typically has a cross section that conforms to the desired main body shape so further forming of this main body portion of the blank is minimal. In general, thedie 300 is formed according to conventional techniques, using known materials and dimensional sizing for sidewall thickness, etc. - Formation of a finished fastener blank often occurs in several strikes applied by a ram or punches 305 (shown in phantom). The punches are preferably driven by a powerful mechanical actuator (not shown) that strikes the blank under great pressure (see arrow 307) to cause both the blank head and internal blank shape to be formed simultaneously. Several differently shaped punches and/or header dies can be used progressively during formation of the blank and blank head, each with a shape that conforms progressively more closely to that of the finished
blank drive head 102. In this example, that drivehead 102 takes the form of a conventional hex washer head shape as shown above. The tools/punches used herein are considered conventional. - The
die cavity 302 defines the distinct shapes of the blank sections according to each of the embodiments of this invention. Thedie cavity 302 defines a series of shaped sections that form the respective sections of the finished fastener blank through plastic deformation as the initial rod or wire is driven into the die cavity by thepunch 305. The sections each define a multi-lobed cross section having the desired out-of-round configuration as discussed above. The die cavity sections include an elongated main body diecavity section 306 for enclosing the blank's corresponding main body adjacent the opening of the die cavity. The neighboring full-diameter, high out-of-roundthread forming section 312 having a high out-of round is located inwardly of the main body diecavity section 306. Likewise, the tapered thread formingdie cavity section 312 and stabilizing section diecavity section 316 are each located further inwardly, respectively. During the forming process, the rod or wire is seated inwardly as far as it can go. It typically seats onto the front of the full-diameterthread forming section 312. Each strike of the punch or punches, causes the rod or wire tip to deform into the next forward section as it is driven further into the die cavity. A knock-out pin acts as a stop to prevent further inward movement of the blank into thedie cavity 302. This pin is formed from a hardened material according to known processes. It can move axially inwardly and outwardly (double arrow 348) under the force of a mechanical actuator (not shown) of known design. The knock-out pin includes a mechanism that can be locked into position (not shown) so as to maintain its position firmly when it is acting as a stop as shown in Figs 11 and 12. When the blank is to be removed from thedie cavity 302, the knock out pin is moved toward the cavity front opening a sufficient distance to eject the blank. The blank can then be transferred by known techniques to another cavity for further forming or to a threading mechanism or machine for forming of the threads. - Fig. 12 illustrates the die 300 configured to form a blank (200) according to the embodiment detailed in Figs. 8 and 9. This blank is substantially similar in size and shape to the blank (100) described above. However, it omits a stabilizing section at its front. As described above, the knock-out pin can be selectively moved (double arrow 348) toward and away from the front opening of the
die cavity 302. Hence, the knock out pin can be moved by its actuator to selectively occupy the area of the stabilization section diecavity 316. The knock-out pin 330 advantageously has a cross section that matches that of the cavity. To create a blank 100 according to Figs. 6, 7 and 11, the knock-out pin is positioned approximately 1 1/2-3 pitch lengths forwardly of the taperedthread forming section 314. This allows the front tip of the rod or wire 340 to be driven fully into the stabilizingdie cavity section 316. Conversely, when thesection 316 is occupied by the knock-out pin 330, itsfront face 320 provides a stop that prevents the stabilizing section from being formed, creating the alternative finished blank (200). The knock-out pin 330 can be selectively moved to each of these desired stop positions (Fig. 11 or Fig. 12). Appropriate locking mechanisms can be provided to secure thepin 330 in either of the stop positions described above. - The foregoing has been a detailed description of preferred embodiments of the invention. Various modifications and additions can be made without departing from the scope of this invention. For example, the blank can include further forming and stabilizing sections, in addition to the full-diameter forming section detailed herein. A variety of other forming techniques can be used to form blanks, drive heads and thread patterns including fully enveloping dies, cutting tools or rolling dies. Finally, the thread profile depicted herein is of a conventional triangular/straight-line configuration. It is expressly contemplated that a blank according to this invention can be provided with any kind of thread profile including a curved/radius profile, a cupped profile, buttress profile or a square/Acme profile. In addition, while a range of K factors for out-of-round are specified hereinabove for various blank sections, it is expressly contemplated that these values can be varied for applications having particular size, shape and material requirements. The exact K factor can be determined for such an application using data based upon physical tests and experiments on fasteners formed with a given set of properties. Accordingly, this description is meant to be taken only by way of example, and not to otherwise limit the scope of the invention.
Claims (20)
- A self-tapping screw fastener (100, 200) with self-tapping threads (120 - 128, 220 - 228), comprising:(a) a head portion (102, 202) and a tip portion (106, 210);(b) a non-circular main cross-section (150) with an axis (112) and a plurality of radial lobes (154) and valley portions (158) between the radial lobes, said cross-section (150) having an out-of-round attribute K which is a difference between a maximum radial dimension from the axis (112) to a peak of a radial lobe (154) and a second radial least dimension from the axis (112) to a lowest valley portion (158);(c) a pitch 'P' which is an axial distance between corresponding regions of consecutive threads (120);(d) a main body portion (104, 204) of the self-tapping screw fastener adjacent to the head portion (102, 202) and being of a predetermined diameter;(e) a tapered threaded section (108, 206) adjacent the tip portion (106, 210) and of diameter which tapers down from said predetermined diameter towards said tip portion;(f) a first value of K = K1 for the main body portion (104, 204), and a second value of K = K2 for the tapered threaded section (108, 206), in which K2 > K1;(g) an additional threaded section (110, 208) located between the main body portion (104, 204) and the tapered threaded section, and being of axial length (LA, L1A) accommodating at least one thread (162, 230), said additional threaded section (110, 208) having the same predetermined diameter as said main body portion (104, 204) and having a third value of K = K3 where K3 > K1.
- The fastener of claim 1 in which K3 = K2.
- The fastener of claim 1 including a stabilizing section (106) at said tip portion, said stabilizing section having a non-circular cross-section similar to the cross-section of the main body portion (104, 204) and having a diameter not larger than a smallest diameter of the tapered threaded section (108, 206).
- The fastener of claim 3 where said stabilizing section (106) has a value of K substantially the same as K2.
- The fastener of any one of claims 1 to 4 wherein:K1 lies in the range 0.05P to 0.15P;K2 lies in the range 0.2P to 0.3P; andK3 lies in the range 0.2P to 0.3P.
- The fastener of claim 1 further comprising a stabilizing section (106) having stabilizing section lobes (154) with a smaller stabilizing lobe maximum diameter than the main body lobe maximum diameter located axially forward of the tapered threaded section (108).
- The fastener of claim 6 wherein the stabilizing section (106) includes at least two threads (122) located thereon.
- The fastener of claim 1 including at least three radial lobes with corresponding valley portions therebetween.
- A screw fastener blank (100, 200), comprising:(a) a head portion (102, 202) and a tip portion (106, 210);(b) a non-circular main cross-section (150) with an axis (112) and a plurality of radial lobes (154) and valley portions (158) between the radial lobes, said cross-section (150) having an out-of-round attribute K which is a difference between a maximum radial dimension from the axis (112) to a peak of a radial lobe (154) and a second radial least dimension from the axis (112) to a lowest valley portion (158);(c) a main body portion (104, 204) of the screw fastener blank adjacent to the head portion (102, 202) and being of a predetermined diameter;(d) a tapered thread-forming section (108, 206) adjacent the tip portion (106, 210) and of diameter which tapers down from said predetermined diameter towards said tip portion;(e) a first value of K = K1 for the main body portion (104, 204), and a second value of K = K2 for the tapered thread-forming section (108, 206), in which K2 > K1;(f) an additional thread-forming section (110, 208) located between the main body portion (104, 204) and the tapered thread-forming section, said additional thread-forming section (110, 208) having the same predetermined diameter as said main body portion (104, 204) and having a third value of K = K3 where K3 > K1.
- The screw fastener blank of claim 9 in which K3 = K2.
- The screw fastener blank of claim 9 including a stabilizing section (106) at said tip portion, said stabilizing section having a non-circular cross-section similar to the cross-section of the main body portion (104, 204) and having a diameter not larger than a smallest diameter of the tapered thread-forming section (108, 206).
- The screw fastener blank of claim 11 where said stabilizing section (106) has a value of K substantially the same as K2.
- The screw fastener blank of any one of claims 9 to 12 wherein:K1 lies in the range 0.05P to 0.15P;K2 lies in the range 0.2P to 0.3P; andK3 lies in the range 0.2P to 0.3P.
- The screw fastener blank of claim 9 further comprising a stabilizing section (106) having stabilizing section lobes (154) with a smaller stabilizing lobe maximum diameter than the main body lobe maximum diameter located axially forward of the tapered thread-forming section (108).
- The screw fastener blank of claim 9 including at least three radial lobes with corresponding valley portions therebetween.
- A header die (300) for forming the screw fastener blank of any one of claims 9 to 15 having a die cavity (302) having a cross-sectional profile that conforms to the shape of the main body portion (104, 204), the tapered thread-forming section (108, 206) and the additional thread-forming section (110,208) of the fastener blank of any one of claims 9 to 15.
- The header die of claim 16 further including:a selectively positionable knock-out pin (330) that stops linear movement of the blank (100, 200) beyond a predetermined axial point within a cavity (302) of the header die (300) during formation, the knock-out pin being constructed and arranged to selectively uncover and reveal a stabilizing section forming die cavity (316) axially forward of a part (314) of the die cavity (302) that forms the tapered thread-forming section, the stabilizing section forming die cavity (316) being constructed and arranged to form a blank stabilizing section with a lower stabilizing lobe maximum diameter than the main body lobe maximum diameter.
- A method of forming the screw fastener blank (100, 200) of any one of claims 9 to 15 comprising the steps of:driving a piece of wire or rod into a die cavity (302) having a cross-sectional profile that conforms to the shape of the main body portion (104, 204), the tapered thread-forming section (108, 206) and the additional thread-forming section (110, 208) of a fastener blank of any one of claims 9 to 15, to plastically deform the wire or rod; andforming the head portion (102, 202) using a shaped punch and/or header die.
- The method of claim 18 further including the step of:placing a knock-out pin (330) at a predetermined location within the die cavity (302) corresponding to the end of the additional thread-forming section of a screw fastener blank to be formed therein, to prevent further inward movement of the wire or rod into the die cavity during the driving step; andmechanically ejecting the formed screw fastener blank from the die cavity (302) by impact on the end of the knock-out pin distal from the formed screw fastener blank.
- The method of claim 18 or claim 19 when dependent on claim 11 in which the knock-out pin is positioned within the die cavity so as to determine a length of stabilising section (106) at the tip portion of the formed blank.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
US236815 | 1994-05-02 | ||
US09/236,815 US6089806A (en) | 1999-01-25 | 1999-01-25 | Blank for self-tapping fastener |
PCT/IB1999/002060 WO2000043683A1 (en) | 1999-01-25 | 1999-12-28 | Improved self-tapping thread fastener and a blank therefor |
Publications (2)
Publication Number | Publication Date |
---|---|
EP1066473A1 EP1066473A1 (en) | 2001-01-10 |
EP1066473B1 true EP1066473B1 (en) | 2004-06-16 |
Family
ID=22891081
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
EP99959634A Expired - Lifetime EP1066473B1 (en) | 1999-01-25 | 1999-12-28 | Improved self-tapping thread fastener and a blank therefor |
Country Status (7)
Country | Link |
---|---|
US (3) | US6089806A (en) |
EP (1) | EP1066473B1 (en) |
AU (1) | AU1676000A (en) |
DE (1) | DE69918078T2 (en) |
ES (1) | ES2224727T3 (en) |
TW (1) | TW448271B (en) |
WO (1) | WO2000043683A1 (en) |
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JP3469846B2 (en) * | 1999-07-13 | 2003-11-25 | 株式会社メイドー | Guide boss grooved bolt |
AU783705B2 (en) * | 2001-07-02 | 2005-11-24 | Depuy France | Device for securing bits of bone together |
US6494655B1 (en) | 2001-09-13 | 2002-12-17 | Conti Fasteners Ag | Self-tapping screw and method for joining thin workpieces |
US6494656B1 (en) | 2001-09-13 | 2002-12-17 | Conti Fasteners Ag | Self-tapping screw, blank and method for joining thin workpieces and production method for the same |
US6725524B2 (en) * | 2001-11-20 | 2004-04-27 | A. O. Smith Corporation | Electric motor bonding lug apparatus |
US6766573B2 (en) * | 2001-11-20 | 2004-07-27 | A. O. Smith Corporation | Electric motor bonding apparatus |
JP4284405B2 (en) * | 2002-10-17 | 2009-06-24 | 独立行政法人物質・材料研究機構 | Tapping screw and its manufacturing method |
WO2004074698A1 (en) * | 2003-02-20 | 2004-09-02 | Conti Fasteners Ag | Self-tapping screw for use in low ductile materials |
US7267538B2 (en) * | 2003-05-27 | 2007-09-11 | Efrain Morales-Centeno | Adjustable knockout |
US20060090325A1 (en) * | 2004-11-02 | 2006-05-04 | Bernard Jeremy R | Vehicle powertrain joints comprising self-tapping fasteners |
DE102007010221A1 (en) * | 2007-02-28 | 2008-09-04 | Baier & Michels Gmbh & Co. Kg | Screw with a thread forming thread, blank for making the screw and screw connection |
US8419332B2 (en) * | 2007-10-19 | 2013-04-16 | Atlas Bolt & Screw Company Llc | Non-dimpling fastener |
CN102171464B (en) * | 2008-10-02 | 2013-06-19 | 株式会社青山制作所 | Anti cross-thread bolt |
US8529178B2 (en) * | 2010-02-19 | 2013-09-10 | Nucor Corporation | Weldless building structures |
US9004835B2 (en) | 2010-02-19 | 2015-04-14 | Nucor Corporation | Weldless building structures |
ITAN20130104A1 (en) | 2012-06-19 | 2013-12-20 | Norm Civata San Ve Tic A S | SHAPE OF SELF-FORMING THREADED SQUARE ROUNDED FOR FIXING DEVICES AND RELATIVE PRODUCTION METHOD. |
CN106065893A (en) | 2015-04-21 | 2016-11-02 | (株)星宇Hitech | Riveted type spiral drill |
DE202016002905U1 (en) * | 2016-04-29 | 2017-08-02 | Arnold Umformtechnik Gmbh & Co. Kg | screw |
CA2964008C (en) | 2016-05-02 | 2023-10-24 | Nucor Corporation | Double threaded standoff fastener |
US20180051737A1 (en) | 2016-08-18 | 2018-02-22 | Research Engineering & Manufacturing Inc. | High performance thread rolling and thread locking fastener |
JP6434668B1 (en) * | 2018-06-13 | 2018-12-05 | 株式会社トープラ | Male thread member |
CA3145866A1 (en) * | 2019-08-01 | 2021-02-04 | Amrik Singh Garcha | Hybrid thread geometry for threaded fitting |
US11125262B2 (en) * | 2019-10-10 | 2021-09-21 | Research Engineering & Manufacturing, Inc. | Thread forming and thread locking fastener |
USD918701S1 (en) * | 2020-02-03 | 2021-05-11 | Wheel Pros, Llc | Bolt |
USD918700S1 (en) * | 2020-02-03 | 2021-05-11 | Wheel Pros, Llc | Bolt |
USD952450S1 (en) * | 2020-02-03 | 2022-05-24 | Wheel Pros, Llc | Bolt |
DE102020209328A1 (en) * | 2020-07-23 | 2022-01-27 | Arnold Umformtechnik Gmbh & Co. Kg | Screw, usage, procedure and system |
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1999
- 1999-01-25 US US09/236,815 patent/US6089806A/en not_active Expired - Lifetime
- 1999-11-30 US US09/449,645 patent/US6089986A/en not_active Expired - Lifetime
- 1999-12-28 EP EP99959634A patent/EP1066473B1/en not_active Expired - Lifetime
- 1999-12-28 AU AU16760/00A patent/AU1676000A/en not_active Abandoned
- 1999-12-28 DE DE69918078T patent/DE69918078T2/en not_active Expired - Lifetime
- 1999-12-28 WO PCT/IB1999/002060 patent/WO2000043683A1/en active IP Right Grant
- 1999-12-28 ES ES99959634T patent/ES2224727T3/en not_active Expired - Lifetime
-
2000
- 2000-01-11 TW TW089100317A patent/TW448271B/en not_active IP Right Cessation
- 2000-04-28 US US09/560,773 patent/US6261040B1/en not_active Expired - Lifetime
Also Published As
Publication number | Publication date |
---|---|
WO2000043683A1 (en) | 2000-07-27 |
DE69918078D1 (en) | 2004-07-22 |
ES2224727T3 (en) | 2005-03-01 |
DE69918078T2 (en) | 2005-06-16 |
EP1066473A1 (en) | 2001-01-10 |
AU1676000A (en) | 2000-08-07 |
US6089986A (en) | 2000-07-18 |
TW448271B (en) | 2001-08-01 |
US6089806A (en) | 2000-07-18 |
US6261040B1 (en) | 2001-07-17 |
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